The present invention relates to a retrieval technique for video data and, more particularly, to a method of retrieving a video picture and apparatus therefor, which use the function of coding a video picture in units of arbitrary shape objects and are implemented by MPEG4 as an internal standard scheme for video coding in the process of standardization in ISO/IECJTC/SC29/WG11.
According to MPEG4 in the process of standardization, the function of coding a video picture in units of arbitrary shape objects (e.g., a human figure in a picture), which cannot be implemented by MPEG1 or MPEG2 that is a conventional international standard scheme for video coding, can be implemented.
To implement this function, information representing the shape or size of each object is required. This information is coded together with texture information representing changes in luminance and chrominance inside each object, and the resultant data is transmitted or stored.
In a conventional video picture retrieving technique, a change in luminance in a frame (e.g., edge information), change in luminance between frames (e.g., optical flow), or the like is detected, and video sequences are classified by checking changes in these pieces of information. An index for retrieval is assigned to each classified group.
When these processes are performed by a decoder apparatus, a complicated signal processing unit is often required after a reconstructed picture is generated. For this reason, techniques of reducing the processing amount by analyzing a video picture on the basis of motion vector information obtained in the process of generating a reconstructed picture or DCT (Discrete Cosine Transform) coefficient information have also been proposed (for example, Jpn. Pat. Appln. KOKAI Publication Nos. 6-113280 and 7-152779 and Japanese Patent Application No. 8-178778).
In any case, there is a limit to the technique of analyzing video pictures in units of frames and retrieving a video picture, with high precision.
When a video picture is to be retrieved from conventional coded video data (MPEG1 or MPEG2), since retrieval processing is performed in units of frames as minimum units, it is difficult to perform video picture retrieval with high precision.
In contrast to this, according to MPEG4, retrieval processing can be performed in units of objects in each frame as minimum units.